Customizing a range of acceptable tape dimensional stability write conditions

ABSTRACT

Described are embodiments of an invention for customizing the range of acceptable write conditions to a tape of a tape cartridge that contracts or expands laterally based on environmental conditions. The tape drive utilizes servo information to determine if the tape has expanded or contracted from the nominal dimension and to determine the magnitude of the expansion or contraction. In the case of expansion, the magnitude of the determined expansion and the stored maximum amount of contraction must be below a predetermined threshold value to allow a write. In the case of contraction, the magnitude of the determined contraction and the stored magnitude of expansion must be below the same predetermined threshold value to allow a write. If the determined magnitude of contraction or expansion is greater than the stored magnitude of contraction or expansion, respectively, then the new extreme is stored.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/411,152 filed Mar. 2, 2012, which is incorporated by reference.

TECHNICAL FIELD

This invention generally relates to tape drives for moving an elongatetape between a supply reel and a take-up reel, for example for writingand reading data on the elongate tape.

BACKGROUND

As tape capacity increases with each generation, smaller and smallertrack spacing is being demanded along with tighter Track MisRegistration(TMR) requirements and increased linear density such that tape capacitycan be effectively increased without an accompanying loss in dataintegrity. One of the factors that impedes the increased linear densityis the dimensional stability of the tape. Tape Dimensional Stability(TDS) is a measure of the positional stability of the magnetic datatracks relative to each other and is a function of the tape propertiesand environmental effects such as temperature, humidity, tension, andcreep. These environmental factors can cause the tape to expand orcontract laterally, across the width of the tape. Therefore, when a tapeis written to in one environmental extreme and subsequently read from inanother extreme, the position of the data tracks across the tape widthcan change enough to cause signal degradation or read errors.

SUMMARY OF THE INVENTION

Described are embodiments of an invention for customizing the range ofacceptable write conditions to a tape of a tape cartridge that contractsor expands laterally based on environmental conditions. Specifically, inone embodiment, the tape drive utilizes servo information to determineif the tape has expanded or contracted laterally from the nominaldimension. Further, the tape drive utilizes the servo information todetermine the magnitude of the expansion or contraction. The magnitudeof expansion or contraction and previously stored extremes of expansionor contraction are used to determine if a write operation should beallowed to the tape of the tape cartridge. In the case of expansion, themagnitude of the determined expansion and the stored maximum acceptableamount of contraction must be below a predetermined threshold value toallow a write. In the case of contraction, the magnitude of thedetermined contraction and the stored magnitude of expansion must bebelow the same predetermined threshold value to allow a write. Thepredetermined threshold value defines the size of the range of tapedrive acceptable write conditions to the tape of the tape cartridge. Thesum of the maximum acceptable amount of expansion and the maximumacceptable amount of contraction must be at or below the predeterminedthreshold value. If the determined magnitude of contraction or expansionis greater than the stored magnitude of contraction or expansion,respectively, then the new extreme is stored. Thus, if the tapecartridge is in an environment in which the tape tends to contract, thenthe acceptable write conditions skews to a contracting environment.Further, since the range of acceptable write conditions is customized tothe environment experienced by the tape of a tape cartridge, a smallerportion of the TMR budget may be dedicated to tape dimensional stabilitywhile still ensuring read back of data.

For example, an embodiment of a computer implemented method ofestablishing a range of maximum expansion and maximum contraction foracceptable write condition a tape of a tape cartridge includesdetermining if the tape has expanded or contracted in a lateraldirection. If the tape has expanded in the lateral direction then themethod includes determining the amount of expansion and determining ifthe sum of the amount of the expansion and a maximum amount ofcontraction is less than a predetermined threshold value. If the sum isless than the predetermined threshold value then the method stores theamount of expansion as the maximum acceptable amount of expansion. Ifthe tape has contracted then the method includes determining the amountof contraction and determining if the sum of the amount of contractionand the maximum acceptable amount of expansion is less than thepredetermined threshold value. If the sum is less than the predeterminedthreshold value then the method stores the amount of contraction as themaximum acceptable amount of contraction.

In one embodiment, the method also includes disallowing a writeoperation if the sum of the amount of expansion and the maximumacceptable amount of contraction is greater than the predeterminedthreshold value. Further, in one embodiment, the method includesdisallowing a write operation if the sum of the amount of contractionand the maximum acceptable amount of expansion is greater than thepredetermined threshold value.

In one embodiment the sum of the maximum acceptable amount ofcontraction and the maximum acceptable amount of expansion are lessthan, or equal to the predetermined threshold value. In one embodiment,the amount of expansion and the amount of contraction of the tape isdetermined with servo information. Still further, in one embodiment, themaximum acceptable amount of contraction and the maximum acceptableamount of expansion are stored in a cartridge memory of the tapecartridge.

In one embodiment, the method further includes repeating the steps ofdetermining if the tape has expanded or contracted, determining theamount of expansion or amount of contraction, and storing the amount ofexpansion and contraction until the maximum acceptable amount ofcontraction and the maximum amount of expansion sum to the predeterminedthreshold. Further, the maximum acceptable amount of expansion andmaximum acceptable amount of contraction may be initialized at zero atthe time of manufacturer of the tape or when the tape is written to fromthe beginning of tape.

In another embodiment of a tape drive having a head with a plurality ofread and write elements and a plurality of servo elements and a drivecontrol system for moving tape across the head, the tape drive isconfigured to determine if the tape has expanded or contracted in thelateral direction. If the tape has expanded in the lateral directionthen the tape drive is configured to determine the amount of expansionand determine if the sum of the amount of the expansion and a maximumamount of contraction is less than a predetermined threshold value. Ifthe sum is less than the predetermined threshold value then the tapedrive is configured to store the amount of expansion as the maximumacceptable amount of expansion. If the tape has contracted then the tapedrive is configured to determine the amount of contraction and determineif the sum of the amount of contraction and the maximum acceptableamount of expansion is less than the predetermined threshold value. Ifthe sum is less than the predetermined threshold value then the tapedrive is configured to store the amount of contraction as the maximumacceptable amount of contraction.

In another embodiment of a computer program product for establishing arange of maximum expansion and maximum contraction for acceptable writeconditions on tape of a tape cartridge, the computer program productincluding computer readable storage medium having computer readableprogram code embodied therewith, the computer readable program codeincluding computer readable program code configured to determine if thetape has expanded or contracted in the lateral direction. If the tapehas expanded in the lateral direction then the computer readable programcode is configured to determine the amount of expansion and determine ifthe sum of the amount of the expansion and a maximum amount ofcontraction is less than a predetermined threshold value. If the sum isless than the predetermined threshold value then the computer readableprogram code is configured to store the amount of expansion as themaximum acceptable amount of expansion. If the tape has contracted thenthe computer readable program code is configured to determine the amountof contraction and determine if the sum of the amount of contraction andthe maximum acceptable amount of expansion is less than thepredetermined threshold value. If the sum is less than the predeterminedthreshold value then the computer readable program code is configured tostore the amount of contraction as the maximum acceptable amount ofcontraction.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are understood by referring to thefigures in the attached drawings, as provided below.

FIG. 1 is a partially cut away view of an exemplary tape drive with atape cartridge and elongate tape in accordance with an embodiment of theinvention;

FIG. 2 illustrates a view of a tape cartridge accordance with anembodiment of the invention;

FIG. 3 is a schematic view of the tape drive with a tape cartridge andelongate tape in accordance with an embodiment of the invention;

FIG. 4 is a schematic view of a servo format and a magnetic tape head inaccordance with an embodiment of the invention;

FIG. 5 is a schematic view of a portion of tape and a magnetic tape headin accordance with an embodiment of the invention;

FIG. 6 is a schematic view of portions of tape of nominal, expanded andcontracted dimension in accordance with an embodiment of the invention;

FIG. 7 is a flow chart of an exemplary method of establishing a range ofacceptable write conditions in accordance with an embodiment of theinvention;

FIG. 8 is a table illustrating an example of establishing a range ofacceptable write conditions in accordance with an embodiment of theinvention; and

FIG. 9 is a graphical representation illustrating establishing a rangeof acceptable write conditions with the exemplary values of FIG. 8, inaccordance with certain embodiments.

Features, elements, and aspects of the invention that are referenced bythe same numerals in different figures represent the same, equivalent,or similar features, elements, or aspects, in accordance with one ormore embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Described are embodiments of an invention for customizing the range ofacceptable write conditions to a tape of a tape cartridge that contractsor expands laterally based on environmental conditions. Specifically, inone embodiment, the tape drive utilizes servo information to determineif the tape has expanded or contracted laterally from the nominaldimension. Further, the tape drive utilizes the servo information todetermine the magnitude of the expansion or contraction. The magnitudeof expansion or contraction and previously stored extremes of expansionor contraction are used to determine if a write operation should beallowed to the tape of the tape cartridge. In the case of expansion, themagnitude of the determined expansion and the stored maximum acceptableamount of contraction must be below a predetermined threshold value toallow a write. In the case of contraction, the magnitude of thedetermined contraction and the stored magnitude of expansion must bebelow the same predetermined threshold value to allow a write. Thepredetermined threshold value defines the size of the range of tapedrive acceptable write conditions to the tape of the tape cartridge. Thesum of the maximum acceptable amount of expansion and the maximumacceptable amount of contraction must be at or below the predeterminedthreshold value. If the determined magnitude of contraction or expansionis greater than the stored magnitude of contraction or expansion,respectively, then the new extreme is stored. Thus, if the tapecartridge is in an environment in which the tape tends to contract, thenthe acceptable write conditions skews to a contracting environment.Further, since the range of acceptable write conditions is customized tothe environment experienced by the tape of a tape cartridge, a smallerportion of the TMR budget may be dedicated to tape dimensional stabilitywhile still ensuring read back of data.

It will be obvious, however, to one skilled in the art, that embodimentsof the present invention may be practiced without some or all of thesespecific details. In other instances, well known process operations havenot been described in detail to prevent obscuring the embodiments of thepresent invention described herein.

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. While this invention isdescribed in terms of the best mode for achieving this invention'sobjectives, it will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

Magnetic tape includes multiple parallel servo tracks and data tracks. Acorresponding magnetic read/write head includes a number of transducingelements to read from or write to at least some of the trackssimultaneously. To access other tracks, a head assembly is movedlaterally across the width of the tape. The servo tracks on the tapemedia assist the transducing elements to maintain a proper position onthe data tracks.

Multi-track longitudinal recording systems, such as LTO tape drives,typically write tracks wide and read narrow to account for registrationerrors between the time the tape was written and then read. As tracksbecome narrower to allow for increased tape capacity, even minutechanges in the position of a track may lead to track misregistration(TMR) and the inability to properly record to, or read from, a track.

Tape drives generally have a track misregistration budget (TMR budget)which is some percentage of the difference between the write and readwidth. Data error rates can rise drastically whenever the TMR budget isexceeded.

Tape Dimensional Stability (TDS) is a measure of the positionalstability of the magnetic data tracks relative to each other and is afunction of the tape properties and environmental effects such astemperature, humidity, tension, and creep. These environmental factorscan cause the tape to expand or contract laterally, across the width ofthe tape. Some of these dimensional changes are reversible and some arenot. While the read/write head of a tape drive can also experiencedimensional changes from these environmental effects, the changes are onorders of magnitude less than the changes that occur in the media.Therefore, when a tape is written to in one environmental extreme andsubsequently read from in another extreme, the position of the datatracks across the tape width can change enough to cause signaldegradation or read errors. For example, if a tape is written during thetime a tape is subjected to a dry environment and is then subsequentlyread in a high humidity environment, the position of the data tracksacross the tape width can expand enough to cause problems when readingthe previously written data. Herein, the terms expansion and contractionwill refer to expansion and contraction laterally, across the width ofthe tape.

Accordingly, a portion of the TMR budget is dedicated to account for thechanges in position of the data tracks. This portion of the TMR budgetis herein referred to as the TDS budget and defines how much the tape'slateral dimension can change while still expecting that a writeperformed at that condition will be able to be subsequently read. A TDSmaximum value is the largest acceptable expansion value the mediaspecification will allow. The TDS minimum value is the largestacceptable contraction amount the media specification will allow. TheTDS maximum and minimum values defined in the media specificationestablish a range of conditions for the write operations of a tapedrive, and is referred to herein as a TDS range. Further, the TDSmaximum and minimum values are determined such that the tape could bewritten to in one environmental extreme and subsequently read from inanother extreme without signal degradation or read errors. However, thereality is that most tapes are written in one location and also read inthe same location such that there is little change in the environmentalconditions. For example, a tape written in a relatively dry climateusually remains in that climate and is read in that climate. Thus, theprevious range for TDS maximum and minimum values were based on a“worst-case scenario” situation and require a large portion of the TMRbudget to account for all conditions.

The present invention seeks to customize the range of acceptable writeconditions to the tape of a tape that contracts or expands laterallybased on environmental conditions. Further, in one embodiment, thepresent invention detects over time, the various environments the tapehas experienced, and allows write operations up to a maximum, predefinedTDS change without necessarily allowing the full TDS range defined inthe media specification. This enables the tape drive to ensure that allwrite operations are contained within a reliable TMR range.

FIG. 1 illustrates an example of a tape drive 10, which may comprise amagnetic tape data storage drive which writes data 18 to, and reads datafrom, an elongate tape 11 which may comprise magnetic tape data storagemedia. As is understood by those of skill in the art, magnetic tape datastorage drives, also called magnetic tape drives or tape drives, maytake any of various forms. The illustrated magnetic tape drive 10 movesthe magnetic tape 11 along a tape path in the longitudinal direction ofthe tape from a supply reel 12 in a magnetic tape data storage cartridge13 to a take up reel 14. An example of a magnetic tape drive is the IBM®LTO (Linear Tape Open) magnetic tape drive.

The magnetic tape media 11 is moved in the longitudinal direction acrossa read/write and servo tape head system 65. The tape head may besupported and laterally moved by an actuator 17 of a track followingservo system. The magnetic tape media is supported by roller tape guides50, 51, 52, 53, while the magnetic tape media is moved longitudinally.

A typical magnetic tape data storage drive operates in both the forwardand reverse directions to read and write data. Thus, the magnetic tapehead system 65 may comprise one set of read and write elements foroperating in the forward direction and another set for operating in thereverse direction, or alternatively, may have two sets of the readelements on either side of the write elements to allow the same writeelements to write in both directions while the two sets of read elementsallow a read-after-write in both directions.

Referring to FIG. 2, a single reel tape cartridge 13 comprising magnetictape 11, is illustrated wherein the magnetic tape 11 is wound on a hub15 of supply reel 12. A cartridge memory 21 may store informationregarding the data storage cartridge and, for example, comprises atransponder.

Referring to FIG. 3, the magnetic tape drive 10 is illustrated whereinthe magnetic tape 11 is wound on supply reel 12 in the cartridge 13,and, when loaded in the magnetic tape drive 10, is fed between thecartridge reel 15 and a take up reel 14, having hub 29, in the magnetictape drive 10.

The magnetic tape drive 10 comprises a memory interface 22 for readinginformation from, and writing information to, the cartridge memory 21 ofthe magnetic tape cartridge 13. A read/write system is provided forreading and writing information to the magnetic tape, and, for example,may comprise a read/write and servo head system 65 with a servo actuator17 for moving the head laterally across the magnetic tape 11, aread/write servo system 19, and a drive motor system 28 which moves themagnetic tape 11 between the cartridge supply reel 12 and the take upreel 14 and across the read/write and servo head system 65. A control25, read/write servo control 19, and drive motor system 28 form a drivecontrol system 20. The read/write and servo system 19 also controls theoperation of the drive motor system 28 to move the magnetic tape 11across the read/write and servo head system 65 at a desired velocity,and, in one example, determines the lateral location of the read/writeand servo head system 65 with respect to the magnetic tape 11, and, inanother example, determines the longitudinal position of the tape 11 byreading the tape servo tracks, for example, called “LPOS” (LongitudinalPOSition), and in another example, the read/write and servo system 19employs signals from the reel motors to determine the location of theread/write and servo head system 65 with respect to the magnetic tape11. An interface 23 provides communication with respect to one or morehost systems or processors 27, and is configured to receive and to sendinformation externally of the tape drive 10. Alternatively, the tapedrive 10 may form part of a subsystem, such as a library, and may alsoreceive commands from the subsystem, also at interface 23.

A control 25 communicates with the host interface 23, with memoryinterface 22, and communicates with the read/write system, e.g., atread/write and servo system 19. The illustrated embodiments of tapedrives are known to those of skill in the art.

Other types of removable data storage cartridges and tape drives areknown to those of skill in the art. Examples comprise two reel magnetictape cartridges and drives, and comprise optical tape cartridges anddrives.

Referring additionally to FIG. 4, the magnetic tape 11 is formattedduring manufacture with a plurality of servo bands 24 that are parallelto the edges 11 a and 11 b of the magnetic tape 11. The read/write andservo system 19 of FIG. 3 employs the servo signals 24 as read by servoelements 402 and 404 of the read/write and servo head system 65 toposition the read/write and servo head system 65 laterally with respectto the magnetic tape. Further, the multiple read/write elements 406 readand/or write data from data tracks of the data bands 18. No data iswritten in tape guard bands 24 a or 24 b at the tape edges, and the databands 18 each lies between a set of servo bands 24.

FIG. 5 shows a detailed view of a portion 500 of magnetic tape 11 withan exemplary servo head system 65 in accordance with an embodiment ofthe invention. The portion 500 includes a top servo band 24 a and abottom servo band 24 b. In between the tape servo band 24 a and thebottom servo band is data 18. As shown, the top servo band 24 a has acenterline, y_(centertop). In this illustration, the top servo element402 is located at y₁ as the servo head system 65 is moved longitudinalalong the tape 11. The value of y_(top) is the difference between theposition, y₁, of the servo element 402 over the top servo band 24 a andthe centerline, y_(centertop), of the top servo band 24 a. Further, thebottom servo band 24 b has a centerline, y_(centerbottom). In thisillustration, the bottom servo element 404 is located at y₂ as the servohead system 65 is moved longitudinal along the tape 11. Accordingly, thevalue of y_(bottom) is the difference between the position, y₂, of theservo element 404 over the bottom servo band 24 b and the centerline,y_(centerbottom), of the bottom servo band 24 b. The difference betweeny_(top) and y_(bottom) can be used to determine if the tape has expandedor contracted laterally as discussed below with respect to FIG. 6. Itshould be noted that y₁ and y₂ have positive values if they are greaterthan y_(centertop) and y_(centerbottom), respectively. Conversely, y₁and y₂ have negative values if they are less than y_(centertop) andy_(centerbottom), respectively.

FIG. 6 illustrates three portions of tape for comparison purposes. Thefirst portion of tape is at a nominal lateral tape dimension, and isherein referred to as nominal tape 602. The nominal tape 602 is notexpanded or contracted due environmental effects. The second portion oftape has been expanded by environmental effects, and is herein referredto as expanded tape 604. The third portion of tape has been contractedby environmental effects, and is herein referred to as contracted tape606. FIG. 6 shows the servo head element locations y₁ and y₂ as dottedlines. Further, the nominal tape 602 has edges of servo bands 608 and610 for the top servo band and bottom servo band, respectively. Thenominal tape edges 608 and 610 define the nominal tape spacing shown inFIG. 6.

As discussed above, the value of y_(top) is the difference between theposition, y₁, of the servo element 402 over the top servo band 24 a andthe centerline, y_(centertop), of the top servo band 24 a. The value ofy_(bottom) is the difference between the position, y₂, of the servoelement 404 over the bottom servo band 24 b and the centerline,y_(centerbottom), of the bottom servo band 24 b. The distance betweenthe servo head elements 402 and 404 are manufactured to be the samedistance apart as the nominal distance between the same point on twoadjacent servo bands, for example the center of the servo band(y_(centertop) and y_(centerbottom)). Accordingly, the difference,defined here as y_(diff), between the obtained y_(top) and y_(bottom) isequal to zero in the nominal tape that is not expanded or contractedlaterally.

As shown in FIG. 6, because of the expansion of tape, the difference,y_(diff), in the expanded tape portion 604, between the obtained y_(top)and y_(bottom) is less than zero. The amount of expansion is determinedby magnitude of the value of y_(diff) below zero. Further, FIG. 6 alsoillustrates that the portion of tape that is contracted, contracted tape606, difference, y_(diff), between the obtained y_(top) and y_(bottom)is greater than zero. The amount of contraction is determined bymagnitude of the value of y_(diff) above zero. Thus, the read/write andservo system 19 of the tape drive 10 utilizes the information from theservo head elements 402 and 404 to detect the servo head elements' 402and 404 positions with respect to the servo bands 24 and determinewhether the tape 11 has expanded and contracted and to what extent. Inone embodiment, y₁, y₂, y_(top), y_(bottom), y_(centertop),y_(centerbottom), and y_(diff) have units of length which are measuredin microns or scaled microns. However, one of ordinary skill in the artwould understand that y₁, y₂, y_(top), y_(bottom), y_(centertop),y_(centerbottom), and y_(diff) may be measured in any unit of length.

It should be appreciated that such operations can be embodied as amethod implemented as an algorithm having software modules that areimplemented by a computing system. Further, the method can be embodiedas software on any computer readable media, as dedicated firmware, or asa combination of software and firmware, and the like.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wired, optical fiber cable, RF, etc., or any suitable combination of theforegoing. Computer program code for carrying out operations for aspectsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer, other programmable data processing apparatus, orother devices to cause a series of operational steps to be performed onthe computer, other programmable apparatus or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIG. 7 illustrates an embodiment of detecting the magnitude of lateralexpansion or contraction prior to a write operation and determining ifthe conditions are acceptable for writing to the magnetic tape 11 basedon a predetermined threshold value. Further, FIG. 7 illustrates andembodiment of determining a maximum expansion and a maximum contractionfor a range of acceptable write conditions on tape of a tape cartridge.

The value of CM_(min) is the stored amount of maximum acceptablecontraction. Similarly, the value of CM_(max) is the stored amount ofmaximum acceptable expansion so far experienced by the tape media 11. Inone embodiment, CM_(min) and CM_(max) have units of length which aremeasured in microns or scaled microns. However, one of ordinary skill inthe art would understand that CM_(min) and CM_(max) may be measured inany unit of length. The maximum expansion and maximum contractionvalues, CM_(max) and CM_(min), respectively, are initialized to zero. Inone embodiment, CM_(max) and CM_(min) are initialized to zero at thetime of manufacture of the tape 11 or for a tape 11 that is written tofrom the beginning of tape 11 of tape cartridge. Those skilled in theart would understand that when a tape is written to from the beginningof tape, or a “write from zero”, the tape is reformatted. Accordingly,reformatting enables the user to refresh the values CM_(max) andCM_(min). For example, the tape 11 of tape cartridge 13 could bereformatted and the values of CM_(max) and CM_(min) could be refreshedin the event the tape cartridge 13 is moved to a different climate,having different environmental conditions.

In one embodiment, the following algorithm is in the tape drive'smicrocode. Alternatively, in another embodiment, the algorithm is partof the tape drive's hardware. The process begins in step 702. In oneembodiment the process may begin in response to a load of tape cartridge13. In step 702, the magnetic tape drive 10 determines the values ofy_(top) and y_(bottom). As discussed with respect to FIGS. 5 and 6, thevalue of y_(top) is the difference between the measured position, y₁, ofthe servo element 402 over the top servo band 24 a and the centerline,y_(centertop), of the top servo band 24 a. The value of y_(bottom) isthe measured difference between the position, y₂, of the servo element404 over the bottom servo band 24 b and the centerline,y_(centerbottom), of the bottom servo band 24 b.

In step 704 the magnetic tape drive 10 obtains the values stored forCM_(min) and CM_(max). As explained above, the values stored forCM_(min) and CM_(max) are initialized at zero. In one embodiment, thevalues for CM_(min) and CM_(max) are stored in the cartridge memory 21of tape cartridge 13. In this embodiment, a memory interface 22 forreading information from, and writing information to, the cartridgememory 21 may be utilized. In one embodiment, the memory interface is aradio frequency identification tag (RFID tag) to read information from,and write information to cartridge memory 21, as known by those skilledin the art. However, one of ordinary skill in the art would understandthat the values of CM_(min) and CM_(max) could be stored in anothermemory device or on the tape media 11 itself.

In step 706 the tape drive 10 determines the difference, y_(diff),between the determined Y_(top) and y_(bottom). As discussed above withrespect to FIGS. 5 and 6, the difference, y_(diff), between thedetermined y_(top) and y_(bottom) determines whether the tape haslaterally expanded or contracted. In step 708 it is determined ify_(diff) is greater than, or equal to zero. If it is determined thaty_(diff) is greater than, or equal to zero, then the tape has contractedand the process proceeds to step 710. If it is determined that y_(diff)is not greater than, or equal to zero, then the tape has expanded andthe process proceeds to step 720.

In the case where the tape has contracted, in step 710, the magnetictape drive 10 determines if the sum of the absolute value of y_(diff)and the CM_(max) is greater than a predetermined threshold value. In oneembodiment, the predetermined threshold has units of length, measured inmicrons or scaled microns. However, one of ordinary skill in the artwould understand that the predetermined threshold may be measured in anyunit of length. Accordingly, in step 710 the tape drive 10 isdetermining if the amount of contraction and the previously storedmaximum acceptable amount of expansion is greater than a predeterminedthreshold value. In one embodiment, the predetermined threshold value isthe portion of the TMR budget that is allocated for tape dimensionalstability. The predetermined threshold value may be established throughTMR analysis, TDS analysis and testing, or other means known by thoseskilled in the art. If the tape drive 10 determines that the sum of theabsolute value of y_(diff) and the CM_(max) is greater than apredetermined threshold value, then the process flows to step 712. Instep 712 a write command that may be subsequently received will bedisallowed such that the tape drive 10 does not perform a writeoperation.

However, if the tape drive 10 determines that the sum of the absolutevalue of y_(diff) and the CM_(max) is not greater than a predeterminedthreshold value in step 710, then the process flows to step 714. In step714, the magnetic tape drive 10 determines if the absolute value ofy_(diff) is greater than CM_(min.) In this step, the tape drive 10 isdetermining if the amount of contraction of the tape determined in step706 is greater than the amount of contraction that the tape haspreviously experienced, while still allowing a write to the tape 11(e.g. the stored maximum acceptable amount of contraction). If theabsolute value of y_(diff) is greater than CM_(min), thus indicatingthat the amount of contraction is a new maximum acceptable amount ofcontraction, then in step 716 the tape drive 10 sets the value ofCM_(min) as the absolute value of y_(diff) and the process flows to step718. In one embodiment, the tape drive 10 sets the value of the CM_(min)as the absolute value of y_(diff) by storing the value of y_(diff) asCM_(min) in the cartridge memory 21. However, if the tape drive 10determines in step 714 that the absolute value of y_(diff) is notgreater than CM_(min), then no value is set and the process flows tostep 718. In step 718 a write command that may be subsequently receivedis allowed such that the tape drive 10 performs a write to the tape 11.

Returning to step 708, in which the tape drive 10 determines if y_(diff)is greater than, or equal to zero. If it is determined that y_(diff) isnot greater than, or equal to zero, then the tape has expanded and theprocess proceeds to step 720.

In step 720, the magnetic tape drive 10 determines if the sum of theabsolute value of y_(diff) and the CM_(min) is greater than thepredetermined threshold value. Accordingly, in step 720 the tape drive10 is determining if the amount on expansion and the previously storedmaximum acceptable amount of contraction is greater than a setthreshold. If the tape drive 10 determines that the sum of the absolutevalue of y_(diff) and the CM_(min) is greater than the predeterminedthreshold value, then the process flows to step 712. As discussed above,in step 712 the write command that may be subsequently previouslyreceived will be disallowed such that the tape drive 10 does not performa write operation.

However, if the tape drive 10 determines that the sum of the absolutevalue of y_(diff) and the CM_(min) is not greater than a predeterminedthreshold value in step 720, then the process flows to step 724. In step724, the magnetic tape drive 10 determines if the absolute value ofy_(diff) is greater than CM_(max). In this step, the tape drive 10 isdetermining if the amount of expansion of the tape determined in step706 is greater than the amount of expansion that the tape has previouslyexperienced, while still allowing a write to the tape 11 (e.g. thestored maximum acceptable amount of expansion). If the absolute value ofy_(diff) is greater than CM_(max), thus indicating that the amount ofexpansion is a new maximum acceptable amount of expansion, then in step726 the tape drive 10 sets the value of CM_(max) as the absolute valueof y_(diff) and the process flows to step 718. In one embodiment, thetape drive 10 sets the value of the CM_(max) as the absolute value ofy_(diff) by storing the value of y_(diff) as CM_(max) in the cartridgememory 21. However, if the tape drive 10 determines in step 724 that theabsolute value of y_(diff) is not greater than CM_(max), then no valueis set and the process flows to step 718. In step 718 a write commandthat may be subsequently received is allowed, such that the tape drive10 performs a write to the tape 11.

In one embodiment, the process as described in FIG. 7 is repeated forload of tape cartridge 13 by the tape drive 10. Accordingly, for eachload of tape cartridge 13, the tape drive 10 determines if the tape 11of the tape cartridge 13 has laterally expanded or contracted. Inaddition, the tape drive 10 determines the amount of contraction orexpansion the tape 11 has experienced. The tape drive 10 stores theamount of contraction or expansion of the tape 11 if it is a new extremewhich does not cause the range of maximum acceptable amount ofcontraction and the maximum acceptable amount of expansion to exceed thepredetermined threshold value. The tape drive 10 does not allow a writeif the environmental conditions cause the tape 11 to laterally expandgreater than the maximum acceptable amount of expansion or if theenvironmental conditions cause the tape 11 to laterally contract greaterthan the maximum acceptable amount of contraction. Thus, if anenvironment tends to be dry such that the tape tends to contract thetape drive 10 will store larger extremes for the maximum acceptableamount of contraction, CM_(min), rather than the maximum acceptableamount of expansion CM_(max). Accordingly, the range of acceptable writeconditions will skew towards a contracting environment. On the otherhand, if an environment tends to be humid, such that the tape tends toexpand, then the tape drive 10 will store larger extremes for themaximum acceptable amount of expansion, CM_(max), rather than themaximum acceptable amount of contraction CM_(min). Accordingly, therange of acceptable write conditions will skew towards an expandingenvironment.

It should be noted that the predetermined threshold may be defined for aparticular tape media 11 of a tape cartridge 13. The predeterminedthreshold may be different for another tape cartridge 13 due tothickness of the tape, track pitch, tape media vendors, tapegenerations, etc. Accordingly, the tape drive 10 may store apredetermined threshold for one or more varieties of tape media orgenerations of tape media, etc., as necessary. In one embodiment, thepredetermined threshold value may be established through TMR analysis,TDS analysis and testing, or other means known by those skilled in theart. Still further in one embodiment, two separate and differentthresholds; a contraction threshold and an expansion threshold can beestablished. Accordingly, the separate contraction threshold and theexpansion threshold can account can account for tape media that may bemore susceptible to read errors in a particular environment.

In one embodiment, the tape drive 10 can determine the values of y₁, y₂,y_(top), y_(bottom), Y_(centertop), y_(centerbottom), and y_(diff) atthe beginning of tape 11 upon loading the tape cartridge 13. However,one of ordinary skill in the art would understand that the measurementsand determination of y₁, y₂, y_(top), y_(bottom), y_(centertop),y_(centerbottom), and y_(diff) can be performed any where along thelength of the longitudinal tape 11.

The process steps of FIG. 7 are described as being in response toloading a tape cartridge 13. However, one of ordinary skill in the artwould understand that the frequency of the process steps may be morefrequent than every load of tape cartridge 13, or less frequent thanevery load of tape cartridge 13. In one embodiment, the user or themanufacturer can specify the frequency of the performing the processsteps of FIG. 7. For example, a user may want to process steps could beperformed in response to every write request, or at specific locationsalong the length of the tape 11, at specific time intervals such asdays, weeks, months, etc.

Further, in one embodiment a flag may be set to indicate if a writecommand is allowed or disallowed. Accordingly, if the process indicatesthat a write command is disallowed, a flag is set to disallow the writecommand. The tape drive 10 may then check the flag prior to performing asubsequent write command to determine if the command should be allowed.One of ordinary skill in the art would understand that the flag may bestored in a memory (not shown) of the tape drive 10 or other appropriatememory device. In one embodiment the flag remains until the process ofFIG. 7 is repeated. As described above, the process of FIG. 7 isrepeated in response to loading a tape cartridge, or at anothermanufacturer or user desired frequency, as necessary.

FIGS. 8 and 9 illustrates an exemplary determination of a range ofmaximum expansion and maximum contraction for acceptable writeconditions on tape 11 of a tape cartridge 13 in accordance with anembodiment of the invention. Specifically, FIG. 8 illustrates an exampleof utilizing the logic of the flowchart illustrated in FIG. 7 to createa range of maximum expansion and maximum contraction for acceptablewrite conditions on tape 11 of tape cartridge 13. FIG. 9 is a graphicalrepresentation of determining the range of maximum expansion and maximumcontraction for acceptable write conditions on tape 11 of tape cartridge13 in accordance with FIGS. 7 and 8. The steps to determine the dataillustrated in FIGS. 8 and 9 are described in the flowchart FIG. 7. Asdiscussed above, the process may discussed as being performed inresponse to loading tape cartridge 13, however, the process can becarried out at any user's or manufacturer's desired frequency asdiscussed above. In this example, each time the process steps describedin FIG. 7 are followed is referred to as a sample. For the purposes ofbrevity, each sample will not be reviewed in its entirety. Rather, theprocess should be understood in reference to FIGS. 7, 8, and 9.

Turning to FIG. 8, in this example, the predetermined threshold value isset to be 50. As discussed earlier, the predetermined threshold value isthe portion of the TMR budget that is allocated for tape dimensionalstability. The predetermined threshold value may be established throughTMR analysis, TDS analysis and testing, or other means known by thoseskilled in the art. As discussed above, the values stored for CM_(min)and CM_(max) are initialized at zero. As discussed with respect to FIG.7, upon loading tape cartridge 13, in step 706, the tape drivedetermines the determines the difference, y_(diff), between thedetermined y_(top) and y_(bottom). As discussed above, the difference,y_(diff), between the determined y_(top) and y_(bottom) determineswhether the tape has laterally expanded or contracted. For sample 1 itis determined that the y_(diff) is zero. For the purposes of the processdescribed in FIG. 7, since y_(diff) is greater than, or equal to zero,the tape is said to be contracting and the process flows to step 710 asshown in FIG. 7. The magnetic tape drive 10 determines if the sum of theabsolute value of y_(diff) and the CM_(max) is greater than thepredetermined threshold value. Since the sum of the absolute value ofy_(diff) and the CM_(max) is not greater than the predeterminedthreshold value of 50 the process flows to step 714. In step 714, themagnetic tape drive 10 determines if the absolute value of y_(diff) isgreater than CM_(min.) Since the absolute value of y_(diff) is notgreater than CM_(min) the tape drive 10 does not store the value ofCM_(min) and allows a subsequent write command received to proceed. Thevalues of CM_(min), CM_(max), y_(diff), and the sum of CM_(min.) andCM_(max) are shown for sample 1 in FIG. 9.

Turning to the second load of tape cartridge 13, referred to as sample 2of FIG. 8, the values stored for CM_(min) and CM_(max) remain zerobecause the values for CM_(min) and CM_(max) were not stored for thesample 1. For sample 2, the tape drive determines the difference,y_(diff), between y_(top) and y_(bottom). to be 10. Since y_(diff) isgreater than zero the tape 11 is said to be contracting and the magnetictape drive 10 determines if the sum of the absolute value of y_(diff)and the CM_(max) is greater than the predetermined threshold value. Thesum of the absolute value of y_(diff) and the CM_(max) is ten and is notgreater than the predetermined threshold value of 50 so the magnetictape drive 10 determines if the absolute value of y_(diff) is greaterthan CM_(min.) Since the absolute value of y_(diff) is ten, and thus,greater than the previously stored CM_(min) for sample 2, the tape drive10 stores the value of ten for CM_(min) and allows a subsequent writecommand received to proceed. As discussed above, in one embodiment, thevalues for CM_(min) is stored in the cartridge memory 21 of tapecartridge 13. The values of CM_(min), CM_(max), y_(diff), and the sum ofCM_(min.) and CM_(max) are shown for sample 2 in FIG. 9.

The process is similar for third load of tape cartridge 13, referred toas sample 3, shown in FIG. 8. The value stored for CM_(min) is now tenand the value stored for CM_(max) remains zero. The tape drive 10determines y_(diff), to be 15, which is greater than zero. Accordingly,the tape 11 is said to be contracting and the magnetic tape drive 10determines if the sum of the absolute value of y_(diff) and the CM_(max)is greater than the predetermined threshold value of 50. The sum of theabsolute value of y_(diff) and the CM_(max) is 15 and is not greaterthan the predetermined threshold value of 50 so the magnetic tape drive10 determines if the absolute value of y_(diff) is greater thanCM_(min.) Since the absolute value of y_(diff) is 15, and thus, greaterthan the previously stored CM_(min) for sample 3, the tape drive 10stores the value of 15 for CM_(min) and allows a subsequent writecommand received to proceed. The values of CM_(min), CM_(max), y_(diff),and the sum of CM_(min.) and CM_(max) are shown for sample 3 in FIG. 9.

Turning to the fourth load of tape cartridge 13, referred to as sample4, shown in FIG. 8. The value stored for CM_(min) is now 15 and thevalue stored for CM_(max) remains zero. The tape drive 10 determinesy_(diff), to be negative 5, which is not greater than zero. Accordingly,the tape 11 is expanding and the magnetic tape drive 10 determines ifthe sum of the absolute value of y_(diff) and the CM_(min) is greaterthan the predetermined threshold value of 50. The sum of the absolutevalue of y_(diff) and the CM_(max) is 20 and is not greater than thepredetermined threshold value of 50 so the magnetic tape drive 10determines if the absolute value of y_(diff) is greater than CM_(max.)In this case, the absolute value of y_(diff) is 5, and thus, greaterthan the previously stored CM_(max), the tape drive 10 stores the valueof 5 for CM_(max) and allows a subsequent write command received toproceed. The values of CM_(min), CM_(max), y_(diff), and the sum ofCM_(min.) and CM_(max) are shown for sample 4 in FIG. 9.

The process continues for all samples 1 through 10, as explained abovewith respect to FIGS. 7, 8, and 9, to determine a maximum expansionvalue, CM_(max), and a maximum contraction value, CM_(min), for a rangeacceptable write conditions on tape 11 of tape cartridge 13. Turning nowto the tenth load of tape cartridge 13, referred to herein as sample 10.The value stored for CM_(min) is 35 and the value stored for CM_(max) is15. The tape drive determines y_(diff), to be 40, which is greater thanzero. Accordingly, the tape 11 is contracting and the magnetic tapedrive 10 determines if the sum of the absolute value of y_(diff) and theCM_(max) is greater than the predetermined threshold value of 50. Thesum of the absolute value of y_(diff) and the CM_(max) is 55, and istherefore, greater than the predetermined threshold value of 50 so themagnetic tape drive 10 proceeds to step 712 of FIG. 7 and does not allowa subsequent write command to proceed.

The values of CM_(min), CM_(max), y_(diff), and the sum of CM_(min.) andCM_(max) are shown for all samples 1-10 in FIG. 9. As shown in FIG. 9,as the extremes of expansion and contraction are realized for aparticular environment, a maximum expansion and a maximum contractionfor a range of acceptable write conditions is established. FIG. 9illustrates that as the number of samples (e.g. tape cartridge loads)increase, and the maximum amount of expansion, CM_(max), and the maximumamount of contraction, CM_(min), sum to the predetermined thresholdvalue. In subsequent tape cartridge loads, if the amount of expansionand/or contraction (e.g. the magnitude of y_(diff)) is greater than thestored CM_(max), or CM_(min), respectively, then a subsequent writecommand will not be allowed. Thus, the tape drive 10 will only performwrite commands when the measured tape expansion or contraction is withinthe range of CM_(min) and CM_(max) stored within the cartridge memory 21of the tape cartridge 13.

In summary, described herein are embodiments of an invention forcustomizing the range of acceptable write conditions to a tape of a tapecartridge that contracts or expands laterally based on environmentalconditions. Specifically, in one embodiment, the tape drive utilizesservo information to determine if the tape has expanded or contractedlaterally from the nominal dimension. Further, the tape drive utilizesthe servo information to determine the magnitude of the expansion orcontraction. The magnitude of expansion or contraction and previouslystored extremes of expansion or contraction are used to determine if awrite operation should be allowed to the tape of the tape cartridge. Inthe case of expansion, the magnitude of the determined expansion and thestored maximum acceptable amount of contraction must be below apredetermined threshold value to allow a write. In the case ofcontraction, the magnitude of the determined contraction and the storedmagnitude of expansion must be below the same predetermined thresholdvalue to allow a write. The predetermined threshold value defines thesize of the range of tape drive acceptable write conditions to the tapeof the tape cartridge. The sum of the maximum acceptable amount ofexpansion and the maximum acceptable amount of contraction must be at orbelow the predetermined threshold value. If the determined magnitude ofcontraction or expansion is greater than the stored magnitude ofcontraction or expansion, respectively, then the new extreme is stored.Thus, if the tape cartridge is in an environment in which the tape tendsto contract, then the acceptable write conditions skews to a contractingenvironment. Further, since the range of acceptable write conditions iscustomized to the environment experienced by the tape of a tapecartridge, a smaller portion of the TMR budget may be dedicated to tapedimensional stability while still ensuring read back of data.

The flowchart and block diagrams in the above figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

What is claimed is:
 1. A computer program product for establishing arange of maximum expansion and maximum contraction for acceptable writeconditions on tape of a tape cartridge, the computer program productcomprising a non-transitory computer readable storage medium havingprogram code embodied therewith, the program code executable by aprocessor to: determine if said tape has expanded or contracted in alateral direction; if said tape has expanded in said lateral direction,then: determine an amount of expansion; determine if a sum of saidamount of expansion and a maximum acceptable amount of contraction isless than a predetermined threshold value; store said amount ofexpansion as said maximum acceptable amount of expansion if said sum ofsaid amount of expansion and said maximum acceptable amount ofcontraction is less than said predetermined threshold value; and if saidtape has contracted in said lateral direction, then: determine an amountof contraction; determine if a sum of said amount of contraction and amaximum acceptable amount of expansion is less than said predeterminedthreshold value; and store said amount of contraction as said maximumacceptable amount of contraction if said sum of said amount ofcontraction and a maximum acceptable amount of expansion is less thansaid predetermined threshold value.
 2. The computer program product ofclaim 1, further executable by processor to disallow a write operationif said sum of said amount of expansion and said maximum acceptableamount of contraction is greater than said predetermined thresholdvalue.
 3. The computer program product of claim 1, further executable byprocessor to disallow a write operation if said sum of said amount ofcontraction and said maximum acceptable amount of expansion is greaterthan said predetermined threshold value.
 4. The computer program productof claim 1, wherein a sum of said maximum acceptable amount ofcontraction and said maximum acceptable amount of expansion are lessthan, or equal to, said predetermined threshold value.
 5. The computerprogram product of claim 1, wherein said amount of expansion and saidamount of contraction of said tape is determined by servo information.6. The computer program product of claim 1, further executable byprocessor to store said maximum acceptable amount of contraction andsaid maximum acceptable amount of expansion are in a cartridge memory ofsaid tape.
 7. The computer program product of claim 1, furtherexecutable by processor to determine if said tape has expanded orcontracted, determine said amount of expansion or amount of contraction,and store said amount of expansion and contraction until said maximumacceptable amount of contraction and said maximum amount expansion sumto said predetermined threshold.
 8. A tape drive comprising: a headhaving a plurality of read and write elements and a plurality of servoelements; and a drive control system for moving tape across said head;wherein said tape drive is operative to: determine if the tape hasexpanded or contracted from a nominal dimension in a lateral direction;determine an amount of expansion or an amount of contraction of saidtape from a nominal dimension; determine if a first sum of said amountof expansion and a first stored amount of contraction is be greater thana predetermined threshold value if it is determined that the tape hasexpanded, or determining a second sum of said amount of contraction anda first stored amount of said expansion is greater than saidpredetermine threshold value if it is determined that the tape hascontracted; disallow said write request if said first sum or said secondsum is greater than said predetermined threshold value; and allow saidwrite request if said first sum or said second sum is not greater thansaid predetermined threshold value and store said amount of expansion orsaid amount of contraction if said determined amount of expansion isgreater than said first stored amount of said expansion or said amountof contraction is greater than said first stored amount of saidcontraction, respectively.
 9. The tape drive of claim 8, wherein saidamount of expansion and said amount of contraction of said tape isdetermined by servo information.
 10. The tape drive of claim 8, whereinsaid amount of expansion or said amount of contraction is stored in acartridge memory of said tape cartridge.
 11. A computer program productfor evaluating acceptable write conditions on tape of a tape cartridgein response to a write request, the computer program product comprisinga non-transitory computer readable storage medium having program codeembodied therewith, the program code executable by a processor to:determine if the tape has expanded or contracted from a nominaldimension in a lateral direction; determine an amount of expansion or anamount of contraction of said tape from a nominal dimension; determineif a first sum of said amount of expansion and a first stored amount ofcontraction is be greater than a predetermined threshold value if it isdetermined that the tape has expanded, or determining a second sum ofsaid amount of contraction and a first stored amount of said expansionis greater than said predetermine threshold value if it is determinedthat the tape has contracted; disallow said write request if said firstsum or said second sum is greater than said predetermined thresholdvalue; and allow said write request if said first sum or said second sumis not greater than said predetermined threshold value and store saidamount of expansion or said amount of contraction if said determinedamount of expansion is greater than said first stored amount of saidexpansion or said amount of contraction is greater than said firststored amount of said contraction, respectively.
 12. The computerprogram product of claim 11, wherein said amount of expansion and saidamount of contraction of said tape is determined by servo information.13. The computer program product of claim 11, wherein said amount ofexpansion or said amount of contraction is stored in a cartridge memoryof said tape cartridge.